/**
 * Input validation utilities for the captcha-canvas library.
 *
 * This module provides comprehensive validation functions for all CAPTCHA
 * configuration parameters, ensuring that inputs meet security and usability
 * requirements before processing.
 */
export declare const VALIDATION_CONSTRAINTS: {
    readonly MIN_WIDTH: 50;
    readonly MAX_WIDTH: 2000;
    readonly MIN_HEIGHT: 30;
    readonly MAX_HEIGHT: 1000;
    readonly MIN_ASPECT_RATIO: 0.2;
    readonly MAX_ASPECT_RATIO: 5;
    readonly MIN_CHARACTERS: 4;
    readonly MAX_CHARACTERS: 20;
    readonly MIN_FONT_SIZE: 8;
    readonly MAX_FONT_SIZE: 200;
    readonly MIN_OPACITY: 0;
    readonly MAX_OPACITY: 1;
    readonly MAX_DECOYS: 1000;
    readonly MAX_TRACE_SIZE: 20;
    readonly MAX_ROTATION: 90;
};
/**
 * Validates canvas dimensions and throws CaptchaValidationError if invalid.
 *
 * @param width - Canvas width in pixels
 * @param height - Canvas height in pixels
 * @throws {CaptchaValidationError} When dimensions are invalid
 */
export declare function validateDimensions(width: number, height: number): void;
/**
 * Validates color strings and throws CaptchaValidationError if invalid.
 *
 * Supports hex colors (#RGB, #RRGGBB), RGB colors (rgb(r,g,b)),
 * RGBA colors (rgba(r,g,b,a)), and named colors.
 *
 * @param color - Color string to validate
 * @param fieldName - Field name for error reporting
 * @throws {CaptchaValidationError} When color is invalid
 */
export declare function validateColor(color: string, fieldName?: string): void;
/**
 * Validates font names and throws CaptchaValidationError if invalid.
 *
 * @param font - Font name to validate
 * @throws {CaptchaValidationError} When font is invalid
 */
export declare function validateFont(font: string): void;
/**
 * Validates font size and throws CaptchaValidationError if invalid.
 *
 * @param size - Font size in pixels
 * @throws {CaptchaValidationError} When font size is invalid
 */
export declare function validateFontSize(size: number | string): void;
/**
 * Validates opacity values and throws CaptchaValidationError if invalid.
 *
 * @param opacity - Opacity value (0.0 to 1.0)
 * @throws {CaptchaValidationError} When opacity is invalid
 */
export declare function validateOpacity(opacity: number): void;
/**
 * Validates character count and throws CaptchaValidationError if invalid.
 *
 * @param characters - Number of characters
 * @throws {CaptchaValidationError} When character count is invalid
 * @throws {CaptchaSecurityError} When character count is insufficient for security
 */
export declare function validateCharacterCount(characters: number): void;
/**
 * Validates text content and throws CaptchaValidationError if invalid.
 *
 * @param text - Text content to validate
 * @param expectedLength - Expected length of text (optional)
 * @throws {CaptchaValidationError} When text is invalid
 */
export declare function validateText(text: string, expectedLength?: number): void;
/**
 * Validates background image path/URL and throws CaptchaValidationError if invalid.
 *
 * @param background - Background image source (path, URL, or Buffer)
 * @throws {CaptchaValidationError} When background is invalid
 */
export declare function validateBackground(background: string | Buffer): void;
/**
 * Validates rotation angle and throws CaptchaValidationError if invalid.
 *
 * @param rotation - Maximum rotation angle in degrees
 * @throws {CaptchaValidationError} When rotation is invalid
 */
export declare function validateRotation(rotation: number): void;
/**
 * Validates decoy configuration and throws CaptchaValidationError if invalid.
 *
 * @param total - Number of decoy characters
 * @throws {CaptchaValidationError} When decoy count is invalid
 */
export declare function validateDecoyCount(total: number): void;
/**
 * Validates trace line configuration and throws CaptchaValidationError if invalid.
 *
 * @param size - Trace line width in pixels
 * @throws {CaptchaValidationError} When trace size is invalid
 */
export declare function validateTraceSize(size: number): void;
/**
 * Validates complete captcha configuration object.
 *
 * @param config - Configuration object to validate
 * @throws {CaptchaValidationError} When any configuration is invalid
 * @throws {CaptchaSecurityError} When security-related configuration is insufficient
 */
export declare function validateCaptchaConfig(config: any): void;